8.
What is the hybridisation of triplet carbene?
a. sp3
b. sp2
c. sp2 and sp
d. sp
The hybridisation of triplet carbene involves sp² and sp configurations, making option c the correct answer for this CSIR NET question. Triplet carbenes feature two unpaired electrons with parallel spins in different orbitals, unlike singlet carbenes. This distinction affects their geometry and reactivity in organic reactions.
Question Analysis
The question asks: “What is the hybridisation of triplet carbene?” with options a. sp³, b. sp², c. sp² and sp, d. sp. Triplet carbenes (R₂C:) have a central carbon with six valence electrons, forming two σ-bonds while leaving two non-bonding electrons unpaired. These electrons occupy separate orbitals, leading to a triplet spin state (multiplicity 3 per Hund’s rule).
Option Breakdown
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a. sp³: Incorrect, as sp³ hybridization (four hybrid orbitals) suits tetrahedral geometry with four bonds or lone pairs, not seen in carbenes with only two substituents and two non-bonding electrons.
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b. sp²: Partially correct for bent triplet carbenes, where carbon uses three sp² orbitals (two for σ-bonds, one holds one unpaired electron) and a p-orbital holds the other, giving ~120° bond angles.
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c. sp² and sp (Correct): Triplet carbenes adopt both bent (sp², common) and linear/nearly linear (sp, two hybrid orbitals for σ-bonds, two p-orbitals for unpaired electrons, 180° angles) geometries based on substituents and stability.
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d. sp: Applies to linear forms but misses the prevalent bent sp² structure.
Singlet vs Triplet Carbene
Singlet carbenes have paired non-bonding electrons in an sp² hybrid orbital (bent, ~102° angle, electrophilic). Triplet carbenes, more stable due to less electron repulsion, are paramagnetic and diradical-like, reacting stepwise with alkenes to form cyclopropanes. CSIR NET emphasizes this duality, as triplet methylene (CH₂) ground state is triplet.
Exam Relevance for CSIR NET
Mastering carbene hybridization aids questions on reactive intermediates in organic chemistry (Part B/C syllabus). Practice distinguishing via electron configuration: triplet needs orthogonal orbitals for parallel spins. For visuals, bent triplet resembles :CH₂ with sp² carbon.
